I think the reason for using hot stock falls into the "because" category.

A man's wife sent him to the store for a ham. After he bought it, she asked him why he didn’t have the butcher cut off the end of the ham. The man asked his wife why she wanted the end cut off. She replied that her mother had always done it that way and that was reason enough for her. Since the wife’s mother was visiting, they asked her why she always cut off the end of the ham. Mother replied that this was the way her mother did it; Mother, daughter and the husband then decided to call grandmother and solve this three-generation mystery. Grandmother promptly replied that she cut the end of the ham because her roaster was too small to cook it in one piece.

Being a guy who likes to come to his own conclusions, I have done side by side test batches using hot stock and stock straight from the fridge. To me, there was no difference.